The scaling issue in the penetration of concrete targets by rigid projectiles - Revisited

We present a plausible explanation for the scaling issue in the penetration of concrete targets by rigid projectiles, as manifested by the different penetration efficiency of projectiles with various sizes. Our analysis uses the empirically-based size effect for the unconfined compressive strengths of concrete specimens, according to which larger specimens have lower strengths. We define a new (effective) strength parameter for the concrete target, which depends also on the diameter of the projectile. The analysis results in a monotonic relation between the resistance to penetration of a given projectile/concrete pair and the effective compressive strength of this pair. With this relation one can predict the penetration depth of a rigid projectile into a given concrete target, for any impact velocity. We also introduce the concept of equivalent aluminum targets, in order to obtain useful information about penetrations in concrete targets without the complexities involved in their constitutive relations.